The present application relates to a secondary battery in which a cathode contains a lithium transition metal complex compound, a battery pack using the secondary battery, an electric vehicle using the secondary battery, an electric power storage system using the secondary battery, an electric power tool using the secondary battery, and an electronic device using the secondary battery.
In recent years, various electronic devices such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been strongly demanded to further reduce their size and weight and to achieve their long life. Accordingly, as an electric power source for the electronic devices, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed. In these days, it has been considered to apply such a secondary battery to various applications in addition to the foregoing electronic devices. Examples of the various applications include a battery pack attachably and detachably loaded on the electronic devices or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric drill.
As the secondary battery, secondary batteries using various charge and discharge principles have been widely proposed. Specially, a secondary battery using insertion and extraction of an electrode reactant is considered promising, since such a secondary battery provides higher energy density than lead batteries, nickel cadmium batteries, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The cathode and the anode are layered with a separator in between. The cathode contains a cathode active material capable of inserting and extracting an electrode reactant and other material such as a cathode binder. As the cathode active material, in general, a lithium transition metal complex oxide such as LiCoO2 is used.
A composition of the cathode active material which is a supply source of the electrode reactant largely affects performance of a secondary battery. Therefore, several proposals on the composition of the cathode active material have been made. Specifically, in order to obtain superior battery characteristics even in a severe usage environment, Mg exists at a predetermined ratio on the particle surface of a spinel-type lithium transition metal complex oxide (for example, see Japanese Unexamined Patent Application Publication No. 2004-327309). In order to obtain a high capacity and improve low temperature characteristics and the like, covering elements including P, Ni, and the like are provided on the particle surface of a lithium transition metal complex oxide (for example, see International Application Publication WO2006/123572). In order to obtain a high capacity and superior cycle characteristics and to suppress gas generation at the time of high temperature, a covering layer containing element M which is one of Group 2 to Group 13 elements and element X such as P is provided on the particle surface of a lithium transition metal complex oxide (for example, see Japanese Unexamined Patent Application Publication No. 2009-054583).